This present invention relates in general to the field of programmable robotic manipulators, and assist devices that can interact with human operators.
An Intelligent Assist Device (IAD) is in a class of computer-controlled machines that interacts with a human operator to assist in moving a payload. An IAD may provide a human operator with a variety of types of assistance, including supporting payload weight, helping to overcome friction or other resistive forces, helping to guide and direct the payload motion, or moving the payload without human guidance.
Currently, a great deal of assembly and material handling work is done with the help of an x-y overhead rail system. Two exemplary types of x-y overhead rail systems include powered overhead bridge cranes for large loads usually running on I-beams, and unpowered overhead rail systems for smaller loads (e.g., up to a few hundred pounds), running on low-friction enclosed rails. Bridge cranes are typically slow and are usually controlled via pushbuttons. Enclosed rail systems are typically moved by direct application of the user""s force to the payload. Enclosed rail systems are usually faster and more pleasant to use than bridge cranes, and often allow greater operator dexterity.
Getting the payload moving in an x-y overhead rail system is usually done by forward pushing, therefore using the large muscles of the lower body, which are not easily injured. However, controlling the motion of the moving payload can lead to a greater problem, as it requires pulling sideways with respect to the payload""s direction of motion, generally using the smaller and more easily injured muscles of the upper body and back. Stopping the motion of the moving payload can also be problematic as it involves muscles of the upper body and back.
Furthermore, although low-friction x-y overhead designs are used, both the friction and the inertia are greater in the direction in which the payload has to carry with it the whole bridge rail than in the direction in which the payload simply moves along the bridge rail. Thus, anisotropy produces an unintuitive and undesirable response of the payload to applied user forces and often results in the user experiencing a continuous sideways xe2x80x9ctuggingxe2x80x9d as the payload moves, in order to keep it on track. Both steering and anisotropy contribute to ergonomic strain, lower productivity, and a changeover to slow bridge cranes at an unnecessarily low payload weight threshold.
An IAD attempts to combine the powered assistance currently available with bridge cranes, and also the quick and intuitive operator interface available with unpowered rail systems. Ideally, IAD systems also improve upon the performance of unpowered rail systems and provide greater dexterity and speed than powered bridge cranes. However, although current IAD systems attempt to combine the best of overhead systems, many systems present another set of undesirable limitations.
FIG. 1 illustrates an exemplary approach that has been developed for IAD systems in which the payload is hung from a xe2x80x9crigid descenderxe2x80x9d. The rigid descender, also known as a xe2x80x9cmanipulator arm,xe2x80x9d is manufactured by a variety of companies including Creative Ergonomic Systems (Sterling Heights, Mich.), Jomat Industries (Romeo, Mich.), Protomark (Clinton Twp., Mich.), Knight Industries (Auburn Hills, Mich.), and Scaglia S.p.A. (Brembilla, Italy). They are used instead of cables to reach under an overhang (e.g., place a component inside an automobile body, where the roof of the automobile acts as an overhang), to accommodate a shifting center of gravity, or if a high level of rigidity is needed for any other reason depending on the particular application.
In this type of system, a multi-axis force sensor 202 is used to measure operator-applied forces and torques. These measurements are used as an indicator of intent. Sensor 202 may be mounted directly to rigid descender 201 as shown, or to end-effector 203, or to some other location convenient for the operator. Not only can horizontal motion intent be measured in this way, but with a sensor such as the ATI F/T sensor system manufactured by ATI Industrial Automation (Apex, N.C.) or the Cobotics, Inc. multi-axis intent sensor, vertical motion intent as well as intent in the roll, pitch and yaw axes, can be measured. These measurements may, in principle, be used to drive corresponding powered axes. There must, of course, be drive systems associated with those axes (the only drive units shown in FIG. 2 are motorized drive units 204 for horizontal motion).
The operator must grasp an intent sensor 202 rather than either the part itself (not pictured) or the end-effector 203, but there is typically a high degree of correspondence between the motion of the intent sensor and the motion of the part. The operator simply pushes and the part follows. There is also an ergonomic benefit to this approach, in that the forces required are typically much lower than those required in an unpowered system.
However, there are undesirable limitations such as the absence of motorized drive units for axes of motion other than horizontal. For example, rotation about the vertical (yaw) is almost always a requirement when rigid descenders are used, but currently there is not a commercially available drive unit for this particular rotation. Another undesirable limitation is that many commercially available rigid arms incorporate pivoted joints that permit yaw motion and are neither powered nor outfitted with angle sensors. As a consequence, it is not possible to establish the orientation of the intent sensor with respect to the overhead bridge rail without retrofitting those arms with joint angle sensors. This retrofit process is expensive and unique to each particular arm design.
Yet another limitation is that this approach involves xe2x80x9cnon-collocatedxe2x80x9d control. Non-collocation refers to the presence of significant structural flexibility between the point of sensing (e.g., at the intent sensor) and the point of actuation (e.g., at the bridge and runway rails). It is well-known that non-collocated systems are difficult to control and prone to instability. Generally speaking, the control system bandwidth or system response is limited by the lowest-frequency structural mode, which is typically in the 1 Hz range. As a consequence, the responsiveness of the control system may not be dramatically better than that of the unassisted rigid arm. Accordingly, the ergonomic benefits may be limited.
A serial manipulator may be described as a kinematic chain, extending from a ground reference frame, through various links, supports, and through powered or unpowered joints, finally to a payload at the end of the chain. A mounting location of an intent sensor may be referred to as more proximal as it is closer to the ground of the kinematic chain, and more distal as it is closer to the payload of the kinematic chain. Similar terminology may be used for a parallel kinematic mechanism, and for hybrid serial/parallel mechanisms.
The prior art shows a number of undesirable limitations including limited ergonomic benefit, especially for larger payloads. Some systems exhibit potentially unstable behavior, and the inability to adapt easily to the many styles of commercially-available descenders, including cable, chain, and various rigid arm designs. Moreover, many systems lack a standard motorized drive unit for yaw rotation in rigid descenders.
A method and system is provided to measure the motion intent of a human operator in one or more axes. According to the exemplary embodiments, the method and system are implemented on an Intelligent Assist Device (IAD).
According to an aspect of the present embodiment, a system provides intuitive control, preferably such that the human operator has direct and intuitive control over motion speed and direction of a payload. In the exemplary embodiment, the operator can push or twist the a sensor in a particular direction and the IAD would move in that direction. Preferably, the harder the operator pushes, the faster the IAD should move. The sensor is preferably located xe2x80x9cupstreamxe2x80x9d on the system to prevent low frequency vibrational modes from interfering with the sensor signals.
According to another aspect of the present embodiment, a system facilitates ergonomic benefit, even for large loads (e.g., xc2xc ton or larger). In the exemplary embodiment, the human operator can provide modest forces and torques to operate the IAD, and these forces and torques preferably do not scale significantly with payload inertia.
Another aspect of the present embodiment, a system makes possible collocation of intent sensing and actuation for horizontal motions as well as yaw rotation. In the exemplary embodiment, a minimal structural compliance exists between the point of intent sensing and the point at which the motorized drive units act.
Yet another aspect of the present embodiment, the system facilitates compatibility with a wide range of commercially-available descenders. In the exemplary embodiment, existing intent sensors are improved by being compatible with both cable/chain based and rigid descender based systems. Preferably, various types of rigid descenders (e.g., manipulator arms) can be accommodated.
According to an aspect of the present embodiment, a standard motorized drive unit is provided for yaw rotation that may be used with a wide range of commercially-available descenders.
The exemplary embodiments provide flexible ergonomic benefit, because the system preferably involves collocated control, which can make the system easier to control. Moreover, the exemplary embodiments promote stable behavior, including the ability to adapt easily to the many styles of commercially-available descenders, including cable, chain, and various rigid arm designs. Also, the exemplary embodiments can include a standard motorized drive unit for yaw rotation. According to the teachings described herein, the method and apparatus can be utilized by other devices that can use the measured motion intent, if so desired.